Landslides in Mocca, Colombia: Emergency technical report

Landslides in Mocca, Colombia: Emergency technical report

7

Published

7 April 2017

Report on the Municipality of Mocoa - Putumayo

Due to the persistence of some meteorological systems, both in surface and in high levels of the atmosphere, during the month of March rains above the historical values of the month (series 1981-2010) occurred in great part of the country, being constituted the month of March of 2017 in the rainiest of the last years, after the phenomenon of La Niña.

In this way, excess of more than 50% of rain was registered, in about 85% of the stations of the meteorological network of IDEAM in the national territory.

It should be mentioned that the highest amounts of rainfall occurred in sectors of the Pacific region and in specific areas of the piedmont of Meta, Putumayo and Caqueta, as well as in localized areas of Norte de Santander and Antioquia. It is also important to point out volumes between 300 and 400 millimeters in sectors of Cauca, Valle del Cauca, Huila, Tolima, Nariño, Santander and Amazonas (Figure 1).

At the municipal level, the city of Mocoa has historically presented a monomodal regime with greater amounts of rain between May and July, being June the month of greater amounts of precipitation. The climatology represented by data from the IDEAM station at the city's aqueduct facilities indicates that the lowest and highest multiannual averages at Mocoa are respectively January with 200.6 millimeters (mm) and June with 473.5 mm (Figure 2).

Now, the historic series of this station (1981-2010), sets an average for March of 273.1 mm, while the rains of March 2017 reached 499.8 mm; this relationship shows an excess of about 80%. On the other hand, Figure 3 allows to determine that the accumulated of this 2017, is shown above the accumulated "normal" based on the multi-annual averages.

It is important in turn to detail the distribution of daily rainfall for the month of March 2017. From this analysis, it is established that between 18 and 29 precipitations were scarce; with the rains of March 30, accumulated precipitation approached 370 mm, which means that at that time, the excess for the month was light to moderate, while the exceptional volume recorded on March 31 (129 mm) gives rise to the fact that the excess takes on a significant connotation relative to the historical series (figure 4).

Figure 5. Daily distribution of rain during the month of March 2017 (bars) and cumulative precipitation (blue line).
The oval in red illustrates the strong and extraordinary rain of the day 31. Source: IDEAM, April 1, 2017.

Finally, in relation to the rain that fell on the day of the tragedy in Mocoa, it is possible to be noticed that between the 7:00 am of March 31 and 7:00 am of April 1st, period that is constituted like the pluviometric day of March 31, the precipitation volume was 129 mm in total, constituting a high and important value within the series, being one of the highest in a series of more than 30 years. It is important to note that 83% of rainfall on the rainy day of March 31, 2017, that is, 106 mm, occurred in only 3 hours (between 10:00 pm and 1:00 am), constituting an extraordinary event (Figure 6) .

Figure 6. Rainfall distribution during the rainy day of March 31, 2017
Source: IDEAM, April 1, 2017.